1. Field of the Invention
This invention relates to the treatment of impure steam containing a minor proportion of gaseous impurities comprising hydrogen sulfide and more particularly of such steam from a subterraneous source, e.g. geothermal steam, to extract therefrom hydrogen sulfide and other substances contained therein, to improve the utility of the steam as an energy source, to reduce environmental pollution from usage of such steam, to recover valuable byproducts and for other purposes.
2. State of the Art
Steam, including geothermal steam, has been utilized to provide heat energy and/or mechanical energy by way of heat exchangers and prime movers, e.g. steam engines and turbines, in systems usually constituting or employing means for condensing the steam from gaseous to liquid phase.
In the use of geothermal steam for such purposes, equipment corrosion and environmental pollution problems have existed because such steam usually contains small proportions of reactive and noxious contaminants including hydrogen sulfide. Hydrogen sulfide, especially in the presence of moisture, is corrosive to a number of metals used in mechanical and electrical equipment. Hydrogen sulfide dissolves in water and forms a solution of hydrosulfuric acid, and in the presence of moist air tends to oxidize and form sulfurous acid and sulfuric acid solutions, and such solutions are strongly corrosive to many metals. Furthermore, hydrogen sulfide is a noxious gas highly detrimental as a pollutant to the environment. Other contaminant substances which may be present in geothermal steam include carbon dioxide, ammonia, methane, hydrogen and nitrogen, substances comprising boron, mercury and arsenic, and solid particulate matter, some of which can contribute to said corrosion and pollution problems. Also, it is often found that the molar quantity of ammonia in geothermal steam exceeds two times the molar quantity of hydrogen sulfide therein.
In practice, geothermal steam driven turbines and related equipment for producing power have been constructed with special materials intended to resist the corrosive nature of the hydrogen sulfide in the impure geothermal steam and, after use of such steam, the hydrogen sulfide is emitted to the environment causing pollution thereof. Such emission of hydrogen sulfide occurs in part in solution in the cooling water effluent discharged from direct contact condensers and in other part in the noncondensable off-gases effluent from such condensers discharging into the atmosphere. Reported efforts to abate such environmental pollution have been confined (1) to treatment of the hydrogen sulfide-containing cooling water effluent with air, usually in the presence of a dissolved catalyst, to oxidize the hydrogen sulfide in said effluent to elemental sulfur for subsequent separation and disposal, and (2) to treatment of the hydrogen sulfide containing condenser off-gases to oxidize the hydrogen sulfide therein to sulfur or sulfur dioxide, which oxidized form may then be separated by suitable processing for subsequent disposal. Such hydrogen sulfide pollution abatement practices have been found to be expensive, deal only with environmental aspects of the power plant effluents, create catalyst recovery and waste sulfur materials collection and disposal problems, and fail to take advantage of the ammonia contained in geothermal steam.